We propose to continue the largest follow-up study of the health of African-American women yet undertaken, the Black Women's Health Study (BWHS). The overall aim is to assess potential risk and preventive factors for breast cancer, other cancers and important nonmalignant conditions. The purpose of the present grant proposal is to support continued data collection, and analyses that focus on breast cancer. The BWHS cohort was established in 1995 when African-American women aged 21-69 years from across the U.S. completed mail questionnaires, providing data on demographic factors, medical and reproductive history, body size, use of oral contraceptives and other drugs, physical activity, smoking, diet, and other factors. 59,000 women have been followed every two years by mail questionnaires that obtain information on exposures and incident disease, with follow-up rates in each cycle exceeding 80% of the original cohort. Methods for managing the data and validating exposures and outcomes have been established. After follow-up in the proposed grant, 1,400 cases of incident breast cancer will be available for analysis. We will prospectively assess the relation of aspects of body mass index, weight gain, body fat distribution, physical activity, diet, oral contraceptive use, cigarette smoking and hair relaxer use to breast cancer incidence with sufficient power to assess effects in important subgroups, e.g. strata of menopausal status and body mass index. We will also assess the adequacy of the Gall model for predicting breast cancer risk; the model, used to assess the eligibility of women for prevention trials, has never been tested in black women. Although there have been numerous studies of some of these issues in white women, differences in risk factors might modify associations in black women. Importantly, this proposal is not simply a repeat of studies done in white women. It addresses many issues particularly relevant to black women on which data are lacking, such as the influence on breast cancer incidence of high levels of obesity or weight gain, or of physical activity within levels of obesity. The results will fill large gaps in knowledge about risk factors for breast cancer incidence. In addition, the proposed data collection together with DNA being collected under another grant will provide a unique resource for assessing genetic hypotheses concerning cancer and other illnesses in black women.